Method for sealing electronic component mounting substrate, and heat-curable sheet

Abstract

A method for sealing an electronic component mounting substrate including: preparing an electronic component mounting substrate including a substrate and electronic components mounted thereon and having a space between an electronic component and the substrate; placing a thermosetting sheet on the electronic component mounting substrate; and heat-molding the placed thermosetting sheet, to allow a melt of the thermosetting sheet to fill the space between the electronic component and the substrate and be cured. When a distance between the center of the substrate and an optional point P on a frame line that surrounds all the electronic components and minimizes the surrounded area is denoted by Lp, a distance Lq between the center of the substrate and a point Q at which a straight line passing through the point P and the center of the substrate intersects with an outer periphery of the thermosetting sheet is 0.9Lp or more.

1 . A method for sealing an electronic component mounting substrate, the method comprising steps of:
 (a) preparing an electronic component mounting substrate including a substrate and a plurality of electronic components mounted on the substrate and having a space between an electronic component and the substrate;   (b) placing a thermosetting sheet which is smaller in size than the substrate, on the electronic component mounting substrate so as to be in contact with the electronic components; and   (c) heat-molding the placed thermosetting sheet, to allow a melt of the thermosetting sheet to fill the space between the electronic component and the substrate and be cured, wherein   when a distance between a center of the substrate and an optional point P on a frame line that surrounds all of the plurality of electronic components and minimizes a surrounded area is denoted by Lp,   a distance Lq between the center of the substrate and a point Q at which a straight line passing through the point P and the center of the substrate intersects with an outer periphery of the thermosetting sheet is 0.9Lp or more and 1.1Lp or less.   
     
     
         2 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein the distance Lq between the point Q and the center of the substrate is 1.05Lp or less. 
     
     
         3 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein an outer shape of the substrate and an outer shape of the thermosetting sheet are similar to each other. 
     
     
         4 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein
 a height of each of the electronic components is 5 μm to 800 μm, and   a distance of a gap between the electronic components is 5 μm to 2000 μm.   
     
     
         5 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein a height of the space between the electronic component and the substrate is 5 μm to 100 μm. 
     
     
         6 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein the thermosetting sheet has a layer A constituted of a resin composition A having a maximum value of tan δ (loss tangent) of 3 or more as measured at a measurement temperature of 125° C. for a measurement time of 0 to 100 seconds. 
     
     
         7 . The method for sealing an electronic component mounting substrate according to  claim 6 , wherein
 the thermosetting sheet further has a layer B composed of a resin composition B,   the layer B satisfying   a formula: 40,000≤α×E′≤250,000 [Pa/K], where   α represents a thermal expansion coefficient [ppm/K] at 80° C. of a cured product obtained by heating and curing the resin composition B at 175° C. for 1 hour, and   E′ represents a storage modulus [GPa] at 25° C. of the cured product.   
     
     
         8 . The method for sealing an electronic component mounting substrate according to  claim 7 , wherein a ratio B/A of a thickness of the layer B to the layer A is 0.1 to 80. 
     
     
         9 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein the thermosetting sheet contains a filler. 
     
     
         10 . The method for sealing an electronic component mounting substrate according to  claim 9 , wherein a maximum particle diameter of the filler is 35 μm or less. 
     
     
         11 . The method for sealing an electronic component mounting substrate according to  claim 9 , wherein a content of the filler in the thermosetting sheet is 30 to 85 mass %. 
     
     
         12 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein the thermosetting sheet is circular in shape. 
     
     
         13 . A thermosetting sheet for use in the method for sealing an electronic component mounting substrate according to  claim 6 . 
     
     
         14 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein a height of the space between the electronic component and the substrate is 5 μm to 40 μm. 
     
     
         15 . The method for sealing an electronic component mounting substrate according to  claim 9 , wherein an average particle diameter of the filler is 10 μm or less. 
     
     
         16 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein the distance Lp between the point Q and the center of the substrate is 0.91Lp or more. 
     
     
         17 . The method for sealing an electronic component mounting substrate according to  claim 16 , wherein the distance Lp between the point Q and the center of the substrate is 0.93Lp or more. 
     
     
         18 . The method for sealing an electronic component mounting substrate according to  claim 1 , wherein in the step (c), in a pressure atmosphere lower than atmospheric pressure, the placed thermosetting sheet is heated to allow a melt of the thermosetting sheet to fill the space between the electronic component and the substrate and be cured.